1. Field of the Invention
This invention generally relates to wireless communication systems, and more particularly to a wireless telephonic system that determines the location of a subscriber in order to allow direct communication with the subscriber without a preliminary call to the home system.
2. Description of the Related Art
Some wireless telephone systems, including cellular systems operating in the United States, use a "Roamer Access Port" function to allow subscribers to receive incoming calls while roaming. Roaming refers to when a subscriber is in a geographical area not served by a subscriber's home network. According to this function, the subscriber notifies potential callers that he will be roaming and when they want to reach the roaming subscriber they call a "Roamer Access Port" number of a network operating in the current location of the roaming subscriber, i.e., a serving network. They can obtain this number from the subscriber or look it up in a directory. In practice, the caller first dials the "Roamer Access Port" number of the serving network. After receiving a network prompt (e.g., an announcement or a tone), the caller enters a unique Mobile Directory Number (MDN) for the subscriber and waits for the call to be connected. After receiving the MDN, a network controller performs a network-wide or area-wide page for that particular MDN. If the subscriber's phone is powered-on and tuned to one of the paging channels of this network, it will respond with a page response. The controller then assigns a voice/traffic channel for the roaming subscriber's mobile phone and instructs the mobile phone to tune to the assigned voice/traffic channel. The network controller then instructs the mobile phone to alert the subscriber of the incoming call and provides an audible ringing tone to the caller at the same time. When the subscriber answers the call, the controller cuts through the call path and the caller and the subscriber can begin the conversation.
Currently, there are two cellular networks operating in any given city. The cellular subscriber must notify potential callers which network he plans to use for roaming. If the caller does not have this information, he may dial the "Roamer Access Port" number of a network other than the one to which the subscriber's mobile phone is tuned. If the caller knows that there are two networks in a given market, he may look up the "Roamer Access Port" number of the other network and try again. Otherwise, the caller may think that the cellular subscriber has turned off the mobile station or has left that city after receiving the response from the network that the indicated MDN cannot be reached.
One disadvantage of using a Roamer Access Port is that the subscriber must notify callers of his roaming location as well as the time he plans to stay there and the network he will be in. In addition, the callers must obtain the appropriate "Roamer Access Port" number of the network in the cellular subscriber's roaming location.
Other current cellular systems keep track of a subscriber's location by using manual registration/de-registration or automatic registration/de-registration of the mobile phone. Through a manual or automatic registration process the subscriber's home network maintains information on the network currently serving a particular roaming subscriber. Using this type of scheme, callers can reach the subscriber whether he is in his home network or roaming in a serving network.
However, these manual or automatic registration/de-registration systems have several disadvantages. For example, if the subscriber and his home network are based in Massachusetts, then when the caller places the call, it is directed to Massachusetts and the caller must pay for the call from his location to Massachusetts. If the subscriber is not in Massachusetts, but rather is roaming in California, then the home system initiates an additional call to forward the incoming call from Massachusetts to California. The called party must now pay for the phone call from Massachusetts to California.
The extra telephone charges and connections are especially inefficient when the called party is actually located in a zone close to the caller. For example, when the caller is in California, the system first forwards the call to the home network in Massachusetts before routing the call to the called party in California and calling a Massachusetts based party who is currently roaming in California.
Therefore, it is desirable to have a system that does not require a subscriber to inform others in advance where he plans to be roaming or of a roamer access number for a network in that location. It is also desirable to have a system that does not require a call to a subscriber's home system to determine the location of the called party.
The present invention uses and expands on current cellular network systems such as Ames, or GTE's GSM GlobalRoam System which provides an interface between varying worldwide telecommunication standards and forwards received telephone calls to cellular serving sites worldwide. Basic cellular services such as those discussed above will not be elaborated on in this description.